Process for maintaining the composition of viscose precipitating baths containing magnesium sulphate



Patented Feb, 24, 1931 HEISSUED UNITED STATES PATENT OFFICE JOHANN J'OSEF STOCKLY AND RICHARD BARTUNEK, OF TELTOW, NEAR BERLIN, GER- MANY, ASSIGNORS TO THE FIRM VEREINIGTE GLANZSTOFF-FABBIEKEN A.-G., OF

ELIBERFELD, GERMANY PROCESS FOR MAINTAINING THE COMPOSITION OF VISCOSE PRECIPITATING BATES 7' I (CONTAINING MAGNESIUM SULPHATE No Drawing. Application filed November 27, 1928, Serial No. 322,295, andin Germany December 15, 1927.

. In the manufacture of artificial threads, films, small bands and hairs from viscose, sulphuric acid precipitating baths are used, which, in addition to sodium sulphate, also contain magnesium sulphate. Durin use the amount of sulphuric acid contained in the teract dilution by the water, or in evaporatspinning bath becomes reduced, owing to its being neutralized by the alkali of the viscose, and the quantity of the'spinning bath decreases, because a portion of the liquid is carried away by the products, e. g., the threads, and passes into the washing Water. The

amount of sodium sulphate contained inthe bath is, to a certain extent, automatically supplemented inasmuch as this salt is formed continuously by the double decomposition of the alkali with the sulphuric acid. Finally, gradual dilution of the'spinning bath takes place, according to the amount of water contained in the viscose, and in the case of VIS- coses which are not very highly concentrated, not only compensates the loss of volume in the bath, due to the liquid being carried off by the thread, but may even cause the bath to increase in bulk. All these progressive changes which take place in the bath durmg the process of precipitating the viscose must be compensated or reversed, preferably at ntervals but also progressively. Hitherto this has generally been effected by allowing-any ex5 cess of the bath that may form to run away and making up the necessary concentration in sulphuric acid and salts by the addition of these substances to the bath from outside.

In spinning baths of a'simple kind, which contain only sulphuric acid and sodium sulphate as ingredients, it has repeatedly been proposed to employ so-called acid and salt reenerating processes, consisting in evaporat mg the diluted spinning baths, so as to couning the so-called upper baths, or the wash ing baths or subsequent fixing baths contaming the same twosubstances and returmng the concentrated product to the mam spmning bath. When using such regenerating processes smaller quantities of fresh sulphurlc acid and fresh sodium sulphate are required to make up the spinning bath to proper strength or such additions of fresh acid and salt may, in some cases be entirely superfluous. I

Thepresent invention hasfor its object the provision and elaboration of a regeneration process which can be used for spinning baths which are required to contain magnesium sulphate in addition to sulphuric acid or sul phuric acid and sodium sulphate. That with such baths the simple evaporating process does not achieve the desired object has been shown by experiments, both with the main bath and also with the so-called upper baths, washing baths and. the like. It has been found, as a matter of fact, that in the simple evaporation of bath solutions containing both salts simultaneously, the sodium sulphate content increases, disproportionately to the magnesium sulphate content, since fresh sodium sulphate is continuously being formed in the spinning bath. The result is that an excess of sodium sulphate is obtained while it is utterly impossible to keep the magnesium sulphate in solution in the manner required or to recover it. If the regeneration, particu dition to the removed sodium sulphate and thus a proportion of magnesium sulphate is lost with the excess sodium sulphate.

' A practical solution to these difliculties has now been provided in the way hereinafter described and this new method will first be described with reference to examples.

First e'wample Given .a bath solution containing 130 gr.

dium sulphate and then returning it in a concentrated form to the main spinning bath.

If any attempt be made to bring this bath solution into a condition for crystallizing out, by the usual methods of evaporation or cooling down, the desired end will not be achieved, because, in such case, a mixture of sodium sulphate and magnesium sulphate will precipitate. I

The following method of procedure has, however, been found to be efl'ective:

To the above mentioned bath is added 50 gr. per litre of magnesium sulphate, for instance, in the form of Epsom salts. After solution has taken place the bath is cooled down to a temperature of 8 to 10 deg. C. while stirring. In this case about 7 5 gr. of ma nesium sulphate per litre separate out, as psom salt crystals, which are practically free from sodium sulphate. The separated mother liquor is now diluted by about from 5 to 10 per cent of its volume and the solution cooled down while stirring, to about 5 deg. C. During this cooling down sodium sulphate,

. practically free from magnesium sulphate,

separates out in the form of Glauber salts and to the extent of more than 80 gr. of sodium sulphate per litre, so that, after the separation of the crystals, a final liquor remains which,

as compared with the original bath solution resent still contains 95% of H 80 84% of gSO but only 37% of Na SO The remaining final liquor is now concentrated in a suitable concentrating apparatus and returned to the main spinning bath in the concentrated form together with the Epsom salts obtained in the first cooling down process and containing some sulphuric acid, for the purpose of revivification.

In this regeneration process in all 98% of I-LSO and 97% of MgSO are recovered but 63% of Na SO. separated out.

Second example The bath is of the same composition as in the Example 1. This time the bath solution is first diluted'by about 12% so thata bath with about 115 gr. H 80 per litre, 165 gr. MgSO per litre, 115 gr. Na SO per litre is obtained. This solution is now cooled down to about 5 deg. C. At this temperature sodium sulphate free from magnesium sulphate separates out in the form of Glauber salts and in such quantity that only about 47% of sodium sulphate per litre still remains dissolved. The remaining liquor is worked up and used as in Example 1. About the same degree of efliciency is obtained.

T bird example The bath solution to be operated on is com osed of 130 gr. H SO per litre, 240 gr. MggO. per litre, 130 gr. Na SO per litre.

This solution when cooled down to about 8 to 10 deg. C. is capable, without further salts. The filtrate is now diluted meaeae treatment, of separating out magnesium sulphate, free from sodium sulphate, in the form of Epsom salts. At this temperature 7 5 gr. of magnesiumsulphate per litre separate out and a liquor is left which contains: 133 gr. H 80 per litre, 174 gr. ,MgSO per litre, 132 gr. Na SO per litre, a contraction in-the volume of the bath by about 5% taking place at the same time, due to the water of crystallization removed with the Epsom b 5 to 10% and then cooled down to 5 deg. At this temperature sodium sulphate free from magnesium sulphate separates out in the form of Glauber salts, that only about 50 gr. sodium sulphate per litre still remain in the residual liquor. The concentrated final liquor, poor in sodium sulphate, is used, together with the separated Epsom salts, for the revivifica-- tion of the main spinning bath.

F ouxlh example If the bath be composed of 120 gr. H 80 per litre, 160 gr. Mg'SO per litre, 140 gr. Na SO per litre, this solution may be cooled down to 5 deg. C. at once without dilution.

Sodium sulphate free from magnesium sulphate separates out and the concentrated solution, poor in sodium sulphate, is again returned to the main spinning bath.

Fifth example Let it be assumed that the bath SOl'lItlOi'l to be workedup is composed of gr.

H 550 per litre, 200 gr. MgSO per litre,200 '100 (a) 40 gr. per litre magnesium sulphate are added to the bath. After solution has taken place it is cooled down but this time only to a temperature of 10 to 12 deg. C. At this temperatqre, notwithstanding the large amount of sodium sulphate contained in the. solution, Epsom salts practically free from sodium sulphate is precipitated. If this temperature be exceeded a useless mixture containing a large amount of sodium sulphate results. The filtered off solution is then diluted by 5 to 10%, cooled to 5 deg. C. the Glauber salts separated out and thefiltrate concentrated and returned, together with the previously separated Epsom salts, to the main bath.

(b) The solution to be treated is diluted by 15 to 20%, and then at once cooled down to -5 deg. (1., so as to separate out Glauber salts, freed from crystals, evaporated. and aliowfid to run back into the main spinning A at In the above examples the proportions and the procedure to be followed do not vary materially, even though the sulphuric acid content is subjected to considerable fluctuations (increasing, for example, tod50 gr. sulphuric the sulphuric aci acidper litre and more or decreasing to 65 gr. per litre or less In most cases, however, content in the ordinary spinning baths, upper baths and the like fluc- .tuates within these hmits.

The examples clearly show that the magnesium salt content per litre of bath to ,be treated is essentially the deciding factor as to the procedure to be adopted.

If the magnesium sulphate content does not amount to more than about 170 gr. per litre, separation of the Glauber salts may be effected at once by simple cooling.

If the magnesium sulphate content amounts to more than about 220 gr. per litre a portion of the magnesium separated out by a first cooling own to about 8 to 10 deg. C. and then, after suitable dilution, the main portion of the sodium sulphate can be caused to crystallize out by a further coolingldown to 5 deg. C., for example.

If t e magnesium sulphate content lies in the intermediate region between 17 0 and 220 gr. per'litre, the magnesium sulphate content must first be increased by addition. Then the procedure may be as above described. Instead the ma esium sulphate content may be diminishe to less than 170 gr. per litre, by suitable dilution, and then according to the first directions, the separation of the Glauber salts may be begun at once.

If, when the magnesium content is high, the amount of sodium sulphate contained is also large (see Example 5) the first cooling down when separating out the Epsom salts, must not be carried too far (say only to 12 deg. instead of to 8 to 10 deg.) as otherwise sodium sulphate would be precipitated in considerable quantity.

' In an exactly similar manner, the cooling down must be kept within moderate limits when separating out the Glauber salts. If

temperatures of 1() deg. C. and less be reached when the Glauber salts are being separated, there is risk of magnesium sulphate chrystallizing out also if the, amount thereof contained in the solution is considerable. In most cases it is well to be content to cool down to -5 deg. C.

The new process can be used partly for concentrating the main spmning bath and to free it from anexcess of sodium sulphate. It can also be used for the working up of so-called drop baths which drop from spells or rollers or of centrifuge baths which are slung ofi irom spinning centrifuges, or of upper baths wherein spun spools are subsequently fixed or leached out. Ina'ny case the baths to be treated or parts thereof are advantageously worked up according to the process and the concentrated final liquor,

poor in .sodium'sulphate, used with any Epsom salts otherwise separated for the revivification' of the main spinning bath.

sulphate may be,

It must be appreciated thatthe terms sodium sulphate and magnesium sul hate respectively, used in the above speci cation and the claims will also com rise of course vthe aqueous crystalline precipltations, that is to say Epsom salt and Glaubers salt.

What we claim is:

1. For maintaining the composition of sulphuric acid viscose precipitating baths containing magnesium sulphate and sodium sulphate in solution, a process comprising the ollowing steps: crystallizing out at a magnesium sulphate content of more than 220 gr.

per litre part of the magnesium sulphate practically pure form by cooling, separating out the crystalline masses, diluting the resulting liquor and separating out sodium sulphate in ractically pure orm by further lowering. t e temperature, concentrating the resulting mother liquor and adding it with a proportion of magnesium sulphate to the precipitating bath to be revivified.

2. For maintaining the composition of viscose preci itating baths containing in solution in ad ition to sodium sulphate, not less than 220, gr. per litre of magnesium sulphate, the process consisting in cooling down the bath solution to a temperature within the limits 8-10 deg. C. separating the mother liquor from the magnesium sulphate crystals thus formed, diluting the separated mother liquor by an amount within the -10%, cooling to approximately 10 deg. C. separating the resulting llquor from the sodium sulphate crystals thus formed, concooling the bath solution to a temperature within the limits 8-10 deg. C. separating the mother liquor from the ma esium sulphate crystals thus formed, dilut ng the separated mother liquor by an amount withm the hmits.

640%, cooling to approximately -10 deg.

C. separatin the resulting-liquor from the sodium sulp atecrystals thus formed, concentrating said resulting liquor and addingit with a suitable proportion of reviously separated magnesium sul hate to t e precipltating bath to be revivi ed.

In testimony thatwe claim the foregoing V as our invention, we have signed our names.

.JOHANN JOSEF STfiCKLYI'" RICHARD BARTUNEK.

iso

GERTHFZCA @F EQR wee;

Patent Ne 1,793,649. Grted mm 24, 1931, w

meme tesee seesaw m. AL.

It is hereby eertiiiedl that the name at the assignee in the ebove numbered patent was erroneously written and printed as "Ven'eimigte GlaznzstoftJfiiah riekem A.-G,", whereas said name shotfld have been written ane printed as'Vereinigte Glanzsteff-Fahriken A.-G., as shown by the records of aseignm ents in this office:

Page ,3, line 107, claim 3, for the misspelled syllable "diten" read d ition; and that the said Letters Patent shenld be read with these eorrectionstherein that the same may conform to the record of the ease in the Patent Office.

Sied and sealed this 14th day of Aprii, A. 193K.

M. 3. MM,

(See!) Aeting we of Patents. 

